JP2523291B2 - Optical recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium such as a magneto-optical recording medium that records and reproduces information using heat and light such as laser light.

2. Description of the Related Art As one of optical recording media, there is a medium for a magneto-optical memory.

MnBi, MnAlGe, MnSb, MnCuBi, GdFe, TbFe, GdCo, PtCo, TbC are the recording media for magneto-optical memory.
o, TbFeCo, GdFeCo, TbFeO ₃ , GdIG, GdTbFe, GdTbFeCoBi, CoFe
Materials such as ₂ O ₄ are known. These are formed as thin films on a transparent substrate such as plastic or glass by a method such as a vacuum evaporation method or a sputtering method. The characteristics common to these magneto-optical recording media are that the easy axis of magnetization is perpendicular to the film surface, and that the Kerr effect and the Faraday effect are large.

The requirements for such a medium are firstly that the Curie point is about 100 to 200 ° C. and the compensation point is near room temperature. Secondly, defects such as crystal grain boundaries that cause noise are relatively large. Third, it is possible to obtain a magnetically and mechanically uniform film over a relatively large area.

In response to such demands, in recent years, amorphous perpendicular magnetic thin films of rare earth-transition metals have attracted great attention among the above materials.

However, in such a magneto-optical recording medium comprising a rare earth-transition metal amorphous thin film, if the magnetic thin film layer is stored in contact with the atmosphere, the rare earth is selectively corroded or oxidized by oxygen or water in the atmosphere. Recording of information,
Reproduction becomes impossible.

Therefore, in general, much research has been conducted on a structure in which a protective layer is provided on the surface of the magnetic thin film layer on the side of the substrate or the side opposite to the substrate.

Conventionally, as a protective layer for imparting corrosion resistance such as moisture resistance, an attempt has been made to provide an inorganic vacuum vapor deposition film or resin film of silicon monoxide, silicon dioxide, aluminum nitride, silicon nitride, zinc sulfide or the like ( JP-A-58-80142) is disclosed. However, none of these is still satisfactory in terms of corrosion resistance or adhesion between the film and the substrate.

Further, it is disclosed that even when an inorganic glass having a certain composition is used for the protective layer, the durability of the medium, in particular, prevention of moisture permeation, improvement in adhesiveness and the like are observed (Japanese Patent Application Laid-Open No. 2004-242242). 59-52443 and 60-177449).

However, the requirements for durability and corrosion resistance of the magneto-optical recording medium are strict, and even if these are used, the effect is not yet sufficient, and further improvement is desired.

Incidentally, such a problem also applies to an optical recording medium having a so-called phase transition type recording layer.

II Object of the invention The purpose of the present invention is to prevent the deterioration of the recording layer, corrosion resistance,
An object is to provide an optical recording medium having excellent durability.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, the first invention is an optical recording medium having a recording layer on a substrate and having a protective layer on the upper surface and / or the lower surface of the recording layer directly or via an intermediate layer, wherein the protective layer is made of silicon oxide and An optical recording medium containing an alkali metal oxide and aluminum oxide or boron oxide, having a silicon oxide content of 40 to 60 wt% and an alkali metal oxide content of 1.5 to 10 wt%.

A second invention is an optical recording medium having a recording layer on a substrate and having a protective layer on the upper surface and / or the lower surface of the recording layer directly or via an intermediate layer, wherein the protective layer is silicon oxide. , Alkali metal oxides and RO
Containing a metal oxide (R is a divalent metal element) and aluminum oxide or boron oxide, the silicon oxide content is 40 to 60 wt%, the alkali metal oxide content is 1.
The optical recording medium is characterized by being 5 to 10 wt%.

IV Specific Configuration of the Invention Hereinafter, the specific configuration of the present invention will be described in detail.

An embodiment of the magneto-optical recording medium of the optical recording medium of the present invention is shown in FIG.

In FIG. 1, a magneto-optical recording medium 1 of the present invention has a magnetic thin film layer 4 as a recording layer on a substrate 2, and a protective layer made of glass is provided on each of the lower surface and the upper surface of the magnetic thin film layer 4. 31,35 are provided.

In the present invention, at least one of the protective layers 31 and 35 shown in FIG. 1 may be provided, but in consideration of completely protecting the magnetic thin film layer 4, as shown in FIG. It is preferable to provide both.

Such a glassy protective layer 31, 35 of the present invention
Contains 40 to 60 wt% of silicon oxide.

If this value exceeds 60 wt%, it is disadvantageous in terms of corrosion resistance,
Further, if it is less than 40 wt%, it is disadvantageous in terms of the stability of the film.

Such silicon oxides are usually present in the protective layer in the form of SiO ₂ .

Furthermore, the protective layer of the present invention contains an alkali metal oxide in an amount of 1.5 to 10 wt%.

If this value exceeds 10 wt%, the magnetic layer may be adversely affected, and if it is less than 1.5 wt%, the durability is insufficient.

The upper limit of the content of alkali metal oxides is
7.0 wt% is preferable.

Examples of the alkali metal oxide used include Li ₂ O, Na ₂ O, K ₂ O, Rb ₂ O, Cs ₂ O, Fr ₂ O and the like. Among them, Li ₂ O, Na ₂ O and K ₂ O are particularly preferable. Is preferred.

These may be used alone or in combination of two or more. In the protective layer of the present invention, 30 to 59.5 wt% of boron oxide or aluminum oxide is contained as other components.
It is preferable to contain in the range of.

Boron oxide or aluminum oxide is usually present in the protective layer in the form of B ₂ O ₃ , Al ₂ O ₃ , respectively. By containing one of these in a predetermined amount as described above, durability, corrosion resistance, and uniformity are improved.

Further, a part of the content of boron oxide or aluminum oxide used may be replaced with a metal oxide represented by RO (R is a divalent metal element) and contained.

In this case, the content of the metal oxide represented by RO is 50 wt% or less, particularly 10 to 35 wt% in the protective layer. This value is 50
Within the range of wt% or less, the effect of including B ₂ O ₃ or Al ₂ O ₃ can be maintained, and durability and corrosion resistance can be improved.

Specific examples of the metal oxide represented by RO include Ba
O, CaO, MgO, ZnO, PbO, SrO, etc.
It is preferable to use BaO, CaO or SrO.

In the present invention, when the protective layers 31 and 35 are provided on the upper surface and the lower surface of the magnetic thin film layer as shown in FIG. 1, even if the protective layer 31 and the protective layer 35 have the same composition. Also, different compositions may be used within the predetermined range of the present invention.

Further, the composition of only one protective layer may be a predetermined composition within the present invention.

Such a protective layer may be formed by various vapor deposition methods such as sputtering, vapor deposition, ion plating and plasma CV.
D, photo-CVD, especially a multi-source sputtering method using a target having two or more different compositions or a reactive sputtering method using oxygen.

The thickness of such a protective layer is set to 300 regardless of whether it is provided on the upper surface or the lower surface of the magnetic thin film layer.
It is preferably set to 3,000 Å, particularly 500 to 2,000 Å.

If this value is less than 300Å, the weather resistance is poor and
If it exceeds 0Å, the sensitivity will decrease.

When such a protective layer 31 is provided on the substrate 2 and an intermediate layer to be described later is provided thereon, the thickness of the protective layer 31 is
It is preferable that the thickness is about 300 to 1000Å and the thickness of the intermediate layer is about 500 to 1500Å.

Further, as impurities in the protective layer, Ar, N ₂ or the like existing in the film forming atmosphere may enter.

Others, Fe ₂ O ₃ , CuO, Cr ₂ O ₃ , MnO _X , CoO, NiO, As ₂ O ₃
Etc. may be contained up to about 1.0 wt% of the whole.

The magnetic thin film layer 4 used as the recording layer in the present invention is
Information is recorded magnetically by a modulated heat beam or a modulated magnetic field.
It converts light and reproduces it.

As a material of such a magnetic thin film layer 4, an alloy of a rare earth metal such as Gd and Tb and a transition metal such as Fe and Co is preferably formed as an amorphous film by sputtering, vapor deposition or the like.

In this case, the total content of Fe and Co is preferably 65 to 85 at%.

And the balance is substantially rare earth metals, especially Gd and / or
Or Tb.

And, as a preferable example thereof, TbFeCo, GdFeCo, GdTb
FeCo etc.

In these magnetic thin film layers, C is contained in the range of 10 at% or less.
r, Al, Ti, Pt, Si, Mo, Mn, V, Ni, Cu, Zn, Ge, Au
Etc. may be contained.

In addition, as a rare earth element, Sc, Y, and
La, Ce, Pr, Nd, Pm, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu
Etc. may be contained.

The thickness of such a magnetic thin film layer is usually 100 to 10000Å
It is a degree.

Other materials for the recording layer include so-called phase transition type materials such as Te-Se, Te-Se-Sn, Te-Ge, Te-In, Te-Sn, Te-Ge-Sb-
S, Te-Ge-As-Si, Te-Si, Te-Ge-Si-Sb, Te-Ge-Bi, Te-G
e-In-Ga, Te-Si-Bi-Tl, Te-Ge-Bi-In-S, Te-As-Ge-Sb,
Te-Ge-Se-S, Te-Ge-Se, Te-As-Ge-Ga, Te-Ge-S-In, Se-
Ge-Tl, Se-Te-As, Se-Ge-Tl-Sb, Se-Ge-Bi, Se-S (above, Japanese Patent Publication No. 54-41902, Japanese Patent No. 1004835, etc.) TeO _X (JP-A-58) -54338, Te dispersed in the Te oxide described in Patent 974257), TeO _X + PbO _X (Patent 974258), TeO _X + VO _X (Patent 974257), others, Te-Tl, Te -T
l-Si, Se-Zn-Sb, Te-Se-Ga, TeN _{X and} other Te, Se-based chalcogen-based Ge-Sn, Si-Sn and other alloys that cause an amorphous-crystalline transition Ag- There are alloys such as Zn, Ag-Al-Cu, and Cu-Al that cause a color change due to a change in crystal structure, and alloys such as In-Sb that cause a change in crystal grain size.

Such a recording layer may be formed by using a dry coating method such as a vapor deposition method, a sputtering method or an ion plating method. The layer thickness is about 20 nm to 1 μm.

The substrate 2 is made of glass or resin, and preferable resin materials include acrylic resin, polycarbonate resin,
Epoxy resins, polymethylpentene resins and the like can be mentioned.

Among these resins, a polycarbonate resin is preferable in terms of durability, particularly resistance to warping and the like.

In this case, the polycarbonate resin may be any of an aliphatic polycarbonate, an aromatic-aliphatic polycarbonate and an aromatic polycarbonate, but an aromatic polycarbonate resin is particularly preferable. Of these, a polycarbonate resin made of bisphenol is preferable in terms of melting point, crystallinity, handling, and the like. Among them, the bisphenol A type polycarbonate resin is most preferably used.

The number average molecular weight of the polycarbonate resin is 10,0
It is preferably about 00 to 15,000.

The refractive index at 830 nm of such a substrate 2 is usually 1.55 to 1.59.
It is a degree.

Since recording is performed through the substrate 2, the transmittance for writing or reading light is set to 86% or more.

On the magnetic thin film layer formation surface of such a disc-shaped substrate,
A groove for tracking may be formed.

The depth of the groove is about λ / 8n, particularly λ / 6n to λ / 12n (where n is the refractive index of the substrate). The width of the groove is about 0.4 to 2.0 μm.

 Further, a pit for an address may be formed.

Then, it is usually preferable to irradiate the writing light and the reading light from the back surface side of the substrate with the magnetic thin film layer located in the concave portion of the groove as a recording track portion.

With this configuration, the write sensitivity and the read C / N ratio are improved, and the tracking control signal is increased.

Further, other shapes of the substrate may be tapes, drums, and the like.

The protective layer of the present invention described above may be provided directly on the upper surface and / or the lower surface of the magnetic thin film layer 4 as shown in FIG. 1, or may be provided via an intermediate layer.

When the intermediate layer is provided, it is usually particularly preferable to provide it between the protective layer 31 on the substrate side shown in FIG. 1 and the magnetic thin film layer 4.

Examples of such an intermediate layer include compounds containing oxygen, carbon, nitrogen, sulfur, etc., such as SiO ₂ , SiO _X , AlN, Al ₂ O ₃ , and Si ₃ N.
₄ , various dielectric materials such as ZnS, BN, TiO ₂ , and TiN, or other inorganic or organic films can be used.

 Two or more kinds of various dielectric materials may be used.

Further, the organic protective coat layer 5 is usually provided on the protective layer 35 provided on the magnetic thin film layer (on the side opposite to the substrate 2).

As the material of the organic protective coat layer 5, generally, various known organic substances may be used.

More preferably, a radiation-curable compound cured with radiation such as electron beam or ultraviolet ray is used.

Examples of the radiation-curable compound to be used include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds having an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability, such as diallyl phthalate. Examples thereof include monomers, oligomers and polymers having or introduced in the molecule a group capable of being crosslinked by irradiation with radiation such as unsaturated double bonds such as allyl double bonds, maleic acid and maleic acid derivatives, or introduced into the molecule. .

A compound having a molecular weight of less than 2000 is used as the radiation-curable monomer, and a compound having a molecular weight of 2000 to 10,000 is used as the oligomer.

These include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, etc., but particularly preferred ones As, pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate, (Aronix M-7100, M- 5400, M-550
0, M-5700, M-6250, M-6500, M-8030, M-8060, M-8100
Etc., Toa Gosei), urethane elastomer (Nipporan 40
40) Acrylic modified products, or those into which functional groups such as COOH have been introduced, acrylates (methacrylates) of phenol ethylene oxide adducts, acryl groups (methacryl groups) on the pentaerythritol condensed ring represented by the following general formula Or a compound having ε-caprolactone-acryl group, 1) (CH ₂ = CHCOOCH ₂ ) _3- CCH ₂ OH (special acrylate A) 2) (CH ₂ = CHCOOCH ₂ ) _3- CCH ₂ CH ₃ (special acrylate B) 3) [CH ₂ = CHCO (OC ₃ H ₆ ) _n- OCH ₂ ] _3- CCH ₂ CH ₃ (Special acrylate C) In the formula, a compound of m = 1, a = 2, b = 4 (hereinafter referred to as a special pentaerythritol condensate A), a compound of m = 1, a = 3, b = 3 (hereinafter referred to as a special pentaerythritol condensate B) , M = 1, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate D) , And special acrylates represented by the following general formula.

_{8) CH 2 = CHCOO- (CH} 2 CH 2 O) 4 -COCH = CH 2 ( special acrylate H) 12) AM-N _n -MA A: acrylic acid, M: dihydric alcohol N: dibasic acid (special acrylate L) Further, the radiation-curable oligomer is a polyfunctional oligoester acrylate represented by the following general formula. And acrylic modified urethane elastomers, or those into which a functional group such as COOH is introduced.

Further, a radiation-curable compound obtained by subjecting a thermoplastic resin to radiation-sensitive modification may be used.

As a specific example of such a radiation curable resin, acrylic acid showing an unsaturated double bond having radical polymerizability,
Groups that crosslink or polymerize upon irradiation, such as acrylic double bonds such as methacrylic acid or their ester compounds, allyl double bonds such as diallyl phthalate, and unsaturated bonds such as maleic acid and maleic acid derivatives. Is contained or introduced in the molecule of the thermoplastic resin.

Examples of thermoplastic resins that can be modified into radiation-curable resins include vinyl chloride copolymers, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, fibrin derivatives and the like.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP
Olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiro acetal resins, acrylic resins containing at least one hydroxyl group-containing acrylic ester and methacrylic ester as a polymerization component are also effective.

Organic protective coat layer 5 of such a radiation-curable compound
Has a thickness of 0.1 to 30 μm, more preferably 1 to 10 μm.

If this film thickness is less than 0.1 μm, a uniform film cannot be formed, and the moisture-proof effect in an atmosphere with high humidity is insufficient,
The durability of the magnetic thin film layer 4 is not improved. If it exceeds 30 μm, warpage of the recording medium or cracks in the protective film may occur due to shrinkage during curing of the resin film, which is not practical.

Such a coating film may be usually formed by combining various known methods such as spinner coating, gravure coating, spray coating and dipping. The layer forming conditions of the coating film at this time may be appropriately determined in consideration of the viscosity of the mixture of the coating film composition, the target coating film thickness, and the like.

In order to cure such a coating film to form a protective layer, the coating film may be irradiated with a radiation such as an electron beam or an ultraviolet ray.

When using an electron beam, the radiation characteristics are acceleration voltage
It is expedient to use a radiation accelerator of 100 to 750 KV, preferably 150 to 300 KV, and to irradiate it with an absorbed dose of 0.5 to 20 megarads.

On the other hand, when ultraviolet rays are used, a photopolymerization sensitizer is usually added to the above-mentioned radiation-curable compounds.

The photopolymerization sensitizer may be a conventionally known one,
For example, benzoin methyl ether, benzoin ethyl ether, α-methylbenzoin, α-chlordeoxybenzoin and other benzoin compounds, benzophenone, acetophenone, bisdialkylaminobenzophenone and other ketones, acetolaquinone, phenanthraquinone and other quinones, benzyl disulfide. And sulfides such as tetramethylthiuram monosulfide.
The photopolymerization sensitizer is preferably in the range of 0.1 to 10% by weight based on the resin solid content.

Then, in order to cure the coating film containing such a photopolymerization sensitizer and the radiation-curable compound by ultraviolet rays, various known methods may be used.

For example, a UV bulb such as a xenon discharge tube or a hydrogen discharge tube may be used.

A protective plate 7 is usually provided on the organic protective coat layer 5 with an adhesive layer 6 interposed therebetween.

That is, the protective plate 7 is used in the case of so-called single-sided recording in which recording / reproduction is performed only from the back surface (surface on the side where the magnetic thin film layer 4 is not provided) of the substrate 2.

The resin material of the protective plate 7 is not particularly required to have transparency, and various resins such as polyethylene, polyvinyl chloride, polystyrene, polypropylene,
Polyvinyl alcohol, methacrylic resin, polyamide,
Various types of thermoplastic resin such as polyvinylidene chloride, polycarbonate, polyacetal, fluororesin, phenol resin, urea resin, unsaturated polyester resin, polyurethane, alkyd resin, melamine resin, epoxy resin, silicon resin, etc. are used. It is possible.

Note that various inorganic materials such as glass and ceramic may be used as the protective plate 7.

The shape, dimensions, etc. of this product are substantially the same as those of the substrate 2 described above.

Such a protective plate 7 is bonded via the adhesive layer 6 as described above. The adhesive layer is usually an adhesive such as a hot melt resin and has a film thickness of about 1 to 100 μm.

On the other hand, instead of using the protective plate 7, one set of substrates having the magnetic thin film layer 4, the protective layers 31 and 35, the organic protective coat layer 5 and the like is used, and both magnetic thin film layers are opposed to each other. Then, a so-called double-sided recording type may be used in which the adhesive layers 6 are used for bonding and writing is performed from the back surface side of both substrates. Further, it is preferable that the back surface of the substrate 2 or the protective plate 7 (the surface on the side where the magnetic thin film layer 4 is not provided) is coated with various protective films.

The material of the coating may be the same as the material of the organic protective coating layer 5 described above.

V Effect of the Invention The optical recording medium of the present invention has a protective layer having a predetermined composition on the upper surface and / or the lower surface of the recording layer.

Therefore, the medium of the present invention has extremely excellent durability and corrosion resistance.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention.

[Example 1] A protective layer 31 made of glass having various compositions shown in Table 1 below was provided on a substrate 2 made of a bisphenol A-based optical disc grade polycarbonate resin having a diameter of 13 cm and a thickness of 1.2 mm. In addition, when forming the layer, a sputtering method and, in some cases, a multi-source sputtering method were used. The film thickness was 800 Å for each sample.

21at% Tb, 68at% Fe, 7at% Co,
800 Å thickness of 4at% Cr alloy thin film by sputtering
To form a magnetic thin film layer 4.

The target used was an Fe target on which Tb, Co, and Cr chips were placed.

A protective layer 35 made of glass having various compositions was further formed on the magnetic thin film layer 4.

The composition and film thickness of the protective layer 35 were the same as those of the protective layer 31 used for the predetermined sample.

On the protective layer 35, a coating composition containing the following radiation-curable compound was applied as an organic protective coat layer 5 by spinner coating.

(Coating composition) Polyfunctional oligoester acrylate 100 parts by weight Photosensitizer 5 parts by weight After applying such a coating composition, it was irradiated with ultraviolet rays for 15 seconds to be crosslinked and cured to obtain a cured film.

In this way, various samples as shown in Table 1 below were prepared.

 The following characteristics were measured for this.

(1) Durability Heat cycle test IEC-2-38 (-10 ° C to + 65 ° C, 93% RH) The time at which the bit error rate doubled in the above acceleration test was measured. Under these conditions, film peeling and cracks mainly contributed to the increase in bit error rate.

(2) Corrosion resistance High temperature and high humidity (60 ° C, 90% RH) storage test The time at which the bit error rate doubled in the above acceleration test was measured. Under this condition, mainly pitting (pinhole)
The occurrence of has contributed to the increase of the bit error rate.

 Table 1 shows the results.

In a heat cycle test for evaluating durability, the samples 101 to 104, 107, 111, and 115 to 118 having a protective layer composition with an alkali metal oxide content of 1.5 wt% or more have a double bit error rate. The time exceeded 1000 hours, but the content of alkali metal oxides was 1.0 wt%
Samples 108 and 112 had less than 1000 hours.

Example 2 In the sample 101 (Table 1) of Example 1, the composition of the magnetic thin film layer was Tb 21%, Fe 72%, Co 7%, and the magnetic thin film layer 4 was used.
ZnS sputtered film (8
Sample 201 was prepared in the same manner as Sample 101 except that the thickness of 00Å was formed.

This sample 201 was tested for durability and corrosion resistance as described above.

As a result, it was confirmed that the durability and corrosion resistance of Sample 201 were almost the same as those of Sample 101, respectively.

In addition, such an effect is caused by the phase transition type Te-Ge, TeO _X , T
The same was realized in the recording layer such as e-Se.

 From the above results, the effect of the present invention is clear.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium showing an example of the present invention. Explanation of symbols 1 ... Magneto-optical recording medium, 2 ... Substrate, 31,35 ... Protective layer, 4 ... Magnetic thin film layer, 5 ... Organic protective coat layer, 6 ...
… Adhesive layer, 7 …… Protective plate

Claims (2)

(57) [Claims] 1. An optical recording medium having a recording layer on a substrate and having a protective layer on the upper surface and / or the lower surface of the recording layer directly or via an intermediate layer, wherein the protective layer is silicon oxide and an alkali metal. Contains oxides and aluminum oxide or boron oxide, silicon oxide content of 40-60 wt%, alkali metal oxide content
An optical recording medium characterized by being 1.5 to 10 wt%. 2. An optical recording medium having a recording layer on a substrate and having a protective layer on the upper surface and / or the lower surface of the recording layer directly or via an intermediate layer, wherein the protective layer is silicon oxide or an alkali metal. Oxides and metal oxides represented by RO (R is a divalent metal element) and aluminum oxide or boron oxide, the silicon oxide content is 40-60 wt%, the alkali metal oxide content is 1.5
An optical recording medium, characterized in that the content is up to 10 wt%.